The present invention relates to an anode material made of an alloy or a compound including at least either tin (Sn) or silicon (Si), and a battery using the anode material.
In recent years, as mobile devices have higher performance and more functions, secondary batteries with higher capacity used as power sources of the mobile devices have been desired. A secondary battery which meets the requirement is a lithium-ion secondary battery. However, in a currently widely used lithium-ion secondary battery using lithium cobalt oxide as a cathode and graphite as an anode, its battery capacity is in a saturation state, so it is extremely difficult to significantly increase the capacity.
Under the circumstances, as an anode material capable of achieving a higher capacity, tin and silicon which form an alloy with lithium, and an alloy thereof have been widely researched. However, they have the following problem. When they are bonded with and dissociated from lithium (Li) during charge and discharge, they are expanded and shrunk, so they are cracked into small pieces whenever charge and discharge are repeated. Thereby, they have poor cycle characteristics. Therefore, attempts to prevent the expansion of the alloy during charge by adding an element which does not form an intermetallic compound with lithium have been made (for example, refer to Japanese Unexamined Patent Application Publication Nos. Hei 6-325765 and Hei 7-230800).
However, there is a problem that an improvement in the cycle characteristics is not sufficient even if the element is added.